1. Field of the Invention
This invention concerns a pigment compositions and processes for manufacturing the same, and more particularly pigment compositions containing elemental carbon.
2. Description of the Prior Art
The use of elemental carbon in its various forms such as carbon black, channel black, lamp black etc., as a black pigment is widespread but certain disadvantages of this material are encountered in its use. Firstly the cost of manufacturing such elemental carbons has increased considerably in recent years since the burning of petroleum or natural gas is often involved in their manufacture.
Secondly, in use as a paint pigment dispersed in a vehicle, the oil absorption characteristic of such materials as carbon black, channel black, etc., is quite high. The oil absorption characteristic is related to the amount of vehicle required to completely coat and disperse the carbon particles, and since such vehicles are typically petroleum based they likewise are quite expensive. This high oil absorption comes about because of the very fine particle size of these forms of carbon generally of a size range of 1/100 of a micron, and the resulting great surface area of a given quality of carbon.
This fine particle size also creates difficulties in manufacturing pigments containing such carbon materials inasmuch as this requires rather sophisticated equipment in order to produce proper dispersal of the particles in the vehicle, this equipment necessitating highly skilled personnel to operate and considerable capital expense.
These disadvantages associated with carbon pigmenting have heretofore been recognized by those skilled in the art and attempts have been made from time to time, in the past, to provide an elemental carbon containing pigments comprised of carrier bodies of a larger particle size, upon which has been deposited elemental carbon.
One such approach is disclosed in U.S. Pat. No. 2,258,438, involving a method of producing such a particulate black pigment by heating at high temperatures a spent filtering clay medium which had been used to filter oil, with the heat producing destructive distillation of the oil leaving a carbon residue on the clay particles, the resulting carbon-clay material then being ground in a ball mill and then transported to a separator to sort the various particle sizes and remove the large grains present in the large clay.
A similar approach is described in U.S. Pat. Nos. 1,424,729 and 1,609,120, which disclose a method of destructive distillation of oil coated clay or silica particles to produce particles covered with elemental carbon.
Another such approach is described in U.S. Pat. No. 2,156,591 in which a material referred to as "silica black" or "carburized silica" is created by mixing a coal tar material with a finely divided diatomaceous earth, a subsequent destructive distillation of the tar similarly producing a carbonization of the tar and leaving a coating on the silica particles. A residue of approximately 8% to 10% by volume remains in the mixture.
A further approach is described in U.S. Pat. Nos. 3,094,428; 3,662,650 and 3,390,006 in which a method is disclosed in which is formed a mixture of silica and carbon black in a slurry which is dried and ground to produce a filler mixture which is utilized in improving the physical qualities of rubber.
All of these processes, however, are relatively expensive to carry out inasmuch as they involve high temperature heating to produce destructive distillation, or slurry mixing processes and subsequent drying, both of these processes requiring rather extensive equipment to carry out. Furthermore, certain nondesirable residues are typically produced in the instance of the spent filtering media approach as described, and the quantity of such materials available for manufacturing pigment would be somewhat limited and depend on the usages in other industries. It would also involve the expense of handling, shipping, recovering of the filtering materials.
It is accordingly an object of the present invention to provide a pigment or filler material containing elemental carbon of improved body and oil absorption characteristics which does not contain undesirable residues tending to affect the tinting power, body or other characteristics of the resulting composition.
A further object of the present invention is to provide a process for making such a pigment which does not involve elaborate manufacturing processes such as destructive distillation, burning, slurry forming etc., nor the capital equipment necessary for such processes.